The invention generally relates to memory devices, and more specifically to internally-refreshing dynamic random access memory (DRAM).
Many modern electronic devices contain digital memory (e.g., a dynamic random access memory, DRAM). Each memory may be used to store information for a digital device. Users of such electronic devices typically desire a fully functional device that is as inexpensive as possible. To that end, there is a push to replace more expensive Flash memory and static random access memory (SRAM) with less expensive DRAM memory.
DRAM devices store data in memory elements that have an associated retention time. DRAM devices are referred to as dynamic because if the memory elements are not refreshed within the retention time, the data stored in the memory element may be lost. For example, a DRAM usually stores data in capacitors which, due to leakage, gradually discharge and need to be periodically refreshed in order to prevent data loss. Accordingly, the memory elements are periodically refreshed.
During typical DRAM operating conditions, a memory controller connected with a DRAM device generates periodic signals to refresh the memory elements in order to retain the data. However, when DRAM is used in a system to emulate other types of memory, such as Flash and SRAM, the system's memory controller may not be configured for DRAM operation, and thus may be unable to generate the periodic refresh signals.
Accordingly, what is needed is a method and apparatus for refreshing a DRAM device.